Re: Proposal - improve eqsel estimates by including histogram bucket numdistinct statistics - Mailing list pgsql-hackers

From Jeff Davis
Subject Re: Proposal - improve eqsel estimates by including histogram bucket numdistinct statistics
Date
Msg-id 1213024269.7180.104.camel@jdavis
Whole thread Raw
In response to Re: Proposal - improve eqsel estimates by including histogram bucket numdistinct statistics  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
On Sun, 2008-06-08 at 19:03 -0400, Tom Lane wrote:
> Your argument seems to consider only columns having a normal
> distribution.  How badly does it fall apart for non-normal
> distributions?  (For instance, Zipfian distributions seem to be pretty
> common in database work, from what I've seen.)
> 

If using "Idea 1: Keep an array of stadistinct that correspond to each
bucket size," I would expect it to still be a better estimate than it is
currently, because it's keeping a separate ndistinct for each histogram
bucket.
Regards,    Jeff Davis



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